Get the latest federal technology news delivered to your inbox.

The Department of Homeland Security is emphasizing the threat of a hacker operation that already has attacked U.S. and European energy companies and can disrupt power. The group behind the campaign is affiliated with Russia, according to security researchers.

On Tuesday, DHS reposted and updated for the third time since Wednesday an alert to companies that operate "industrial control systems” -- machines that run critical commercial services.

The so-called Havex "payload" seems to target machines running outdated versions of a widely used specification for connectivity called Open Platform Communications technology.

"Testing has determined that the Havex payload has caused multiple common OPC platforms to intermittently crash," DHS stated. "This could cause a denial-of-service effect," or outage, of "applications reliant on OPC communications."

Citing research from security companies Symantec and F-Secure, DHS said the Havex malicious software "could have allowed attackers to access the networks of systems that have installed" the malware.

The hacker group is alternatively dubbed Energetic Bear and Dragonfly. It has broken into the websites of three control system vendors and dropped the malware into legitimate software updates that its energy customers download. DHS has identified the three vendors on a secure website restricted to companies in key U.S. industries, officials said.

Security startup CrowdStrike first reported the emergence of Energetic Bear in January, describing the group as "an adversary with a nexus to the Russian Federation," that was going after "government and research targets, as well as a large number of energy sector targets."

Symantec, in a paper released Monday, said the prey include companies that operate power grids, electricity generation, and petroleum pipelines, as well as industrial equipment providers.

"Symantec describes the victims as Spain, U.S., France, Italy and Germany, in that order," the DHS alert states.

DHS officials have examined one malware sample that records sensitive operational data, including the kinds of computers and devices connected to a company's network. The spyware gathers information including server name, program IDs, vendor information, running state and server bandwidth, officials said. The malware does not appear to affect devices using newer versions of Open Platform Communications.